Method and agent for treating molten iron and steel



Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE METHOD AND AGENT FOR TREATING MOLTEN IRON AND STEEL James H. Critchett, New York, and Walter Crafts,

Niagara Falls, N. Y., assignors to Electro Metallurgical Company, a corporation of West Vir- The invention relates to the treatment of molten iron and steel to promote a fine grain structure and freedom from deleterious impurities. This application is in part a continuation of our 6 application Serial No. 201,931, filed April 14, 1938.

During manufacture, steels become contaminated with certain oxides and occluded gases, which, if not substantially removed or rendered innocuous, detrimentally affect the soundness and physical properties of the finished steel. To overcome the deleterious efiects of such impurities, an addition of ferrosilicon or ferromanganese, or both, as deoxidizers, is usually made to the steel shortly beTBre casting into ingots or other shapes. For further deoxidation, and to provide an inherently fine-grained steel having inhibited grain growth tendencies at elevated temperatures, a later addition of aluminum is often made to the molten steel.

Aluminum additions, in the amounts, for the purposes, and in the manner described above, tend to produce a steel containing deleterious types and quantities of non-metallic inclusions. It has been proposed to substitute for the alumi- 25 num other agents, such as vanadium, or titanium, but none of these elements is entirely satisfactory. Vanadium is usually too expensive to add in an amount sufiicient to produce the desired results, and titanium as heretofore used tends to produce a steel containing numerous objectionable non-metallic impurities.

According to the present invention, a steel that is substantially free from deleterious, gaseous or solid nonmetallic impurities and that has improved mechanical properties (including improved impact strength) and excellent fine grain characteristics is produced by adding to the steel while it is molten in the ladle or otherwise shortly before casting, an addition agent containing 25% to 85% (preferably 35% to 55%) of silicon; 1% to 20% calcium, 3% to 20% alumi and at least one metal selected from the group conslsting of titanium and zirconium; remainder iron. The titanium-zirconium group metal or metals constitute a total of at least 3% and not over 20% of the addition agent. Iron is present as an impurity or diluent unavoidably introduced in producing an economical and commercially practicable material, and should not exceed about 50 65%. A preferred addition agent composition contains 45% to 65% silicon, 5% to 15% zirconium, 3% to 15% calcium, 3% to 15% aluminum,

the remainder iron.

One composition within this preferred range which has been especially useful comprises about 4% calcium, 4% aluminum, 10% zirconium, 45% silicon, rest iron. Another comprises about 8% calcium, 8% alumigig 8% zirconium, 40% silicon, rest iron. r"

The constituents of the addition agent are preferably prealloyed in the form of a master al- 10y; but they may be unalloyed or only partially alloyed, and used in the form of a bri uet of comminnted material. Also, some of the constituents ereof may suitably be in the form of easw ily reducible or decomposable compounds such as nitrides, nitrates or mixtures thereof. It is essential, however, that the constituents be closely associated, because successive additions of the I several constituents separately to the steel do not 1 yield the improved results of the invention.

In practicing the process of the invention, we prefer to add to the molten steel being treated a sufficient amount of the addition agent of the invention that the silicon content of the steel is go 1 increased by about 0.25%. The deoxidizing or grain refining power may be controlled and varied by adding more or less than enough ma terial to increase the silicon content of the steels by about 0.25%, or alternatively, the concentra- 25 tion of silicon relative to the other constituents of the addition agent may be varied. If less grain refinement is required, part of the silicon required for deoxidizing may be added as the agent of the invention and part as ordinary ferrosili- 30 con, and if more grain refinement is required, the action of the addition agent may be supplemented by an addition of aluminum or other grain refiner.

The desired composition may be added to the 35 steel in any well known manner, for example, in the furnace, in the gg dle, or in the molten stream dating pouring. Whe n adding' the addition agent to the steel either in the ladle or in the molten stream, an agen'tlgontaining less than about iron should ordinarily be used in order to minimize the chilling effect of the iron. If the agent is added to the steel in the furnace, the iron content of the agent may be greater than 50%. 4

By proper selection of elements, a grain sizegf No. 6 or No. 7 may readily be procured in steels tr according to a method of the invention. Throughout the present specification, grain size? refers to austenitic or inherent grain size deter- 5o mined by the McQuaid-Ehn carburizing test conducted at a temperature of 925 C. for 8 hours, as defined by the A. S. T. M. specification E 1933. The degree of grain refinement or deoxidation of the steel per unit of addition agent added will vary, not only with the combination of elements selected, but also with the type of steel being treated, so that the total amount of agent to be added to the steel for best results must be determined by trial. Ordinarily, this total amount of agent will be less than 5%, and most frequently less than 1%.

While the addition agents of this invention are especially useful in the treatment of steels which are to be hot worked, the invention is also applicable to the treatment of steels which are to be employed as castings. Used for the latter purpose, it has been found that, in many instances, the characteristics of the casting may be improved if the material of the invention is added in an amount which is sufiicient to deoxidize the metal, yet is insufficient to develop harmful inclusions.

Steels treated according to the invention are sound, substantially free from excessive nonmetallic inclusions, and possess improved ductility and shock resistance. Further, the few inclusions distributed throughout such steels are more uniform than diverse, that is, the majority of the inclusions which usually accompany any deoxidizing treatment that produces small grain size are not noticeable in the steels deoxidized in accordance with the invention until a higher degree of grain refinement is attained than that attainable by the addition of aluminum alone.

Calcium, known to be a strong deoxidizing agent, is not ordinarily considered to be per se a grain-refiner; but its presence in the composition of matter of this invention imparts a remarkably improved grain refining power.

This invention includes the several modifications which will readily be apparent to those skilled in the art. For instance, the aluminum may be partially or wholly replaced by magnesium if appropriate modification of the proportions of the other ingredients be made within the percentage ranges indicated above. Moreover, a

small part of the aluminum may be replaced by beryllium, and a part of the calcium may be replaced by barium or strontium.

We claim:

1. A method of treating molten ferrous metal which comprises adding thereto a small but effective amount of an addition agent consisting of 25% to 85% silicon, iron, 1% to 20% calcium, 3% to 20% aluminum, and at least one element selected from the group consisting of titanium and zirconium, the total percentage of the element or elements of such group being between 3% and 15%.

2. A method of treating molten ferrous metal which comprises adding a grain-refining amount less than 1% of an addition agent consisting of to 65% silicon, 3% to 15% calcium, 3% to 15% aluminum, 5% to 15% zirconium, remainder iron.

3. A method of treating molten ferrous metal which comprises adding a grain refining amount less than 1% of an addition agent consisting of approximately 45% silicon, 4% calcium, 4% aluminum, 10% zirconium, rest iron.

4. A method of treating molten ferrous metal which comprises adding a grain refining amount less than 1% of an addition agent containing about silicon, 8% calcium, 8% aluminum, 8% zirconium, rest iron.

5. A composition of matter, suitable for use as an addition agent for treating molten ferrous metal, consisting substantially of 25% to 85% silicon, iron, 1% to 20% calcium, 3% to 20% aluminum, and at least one element selected from the following group consisting of titanium and zirconium, the total percentage of the element or elements from such group being between 3% and 15%,

6. A composition of matter for use as an addition agent for treating molten ferrous metal, containing 35% to 65% silicon, 3% to 15% calcium, 3% to 15% aluminum, and 5% to 15% zirconium, remainder iron.

'7. A composition of matter for use as an addition agent for treating molten ferrous metal, containing about silicon; about 4% calcium, about 4% aluminum, about 10% zirconium, and the remainder iron.

8. An addition agent for deoxidizing molten iron or steel, containing approximately 40% silicon, 8% zirconium, 8% calcium, and 8% aluminum, the remainder iron.

JAMES H. CRITCI-IETT. WALTER. CRAFTS. 

